The curve used until recently by the International Commission for the Conservation of
Atlantic Tunas (ICCAT) to represent the growth of western Atlantic bluefin tuna,
Thunnus thynnus, was estimated using tagging information and modal
sizes that corresponded primarily to very young fish (ages 1–3, primarily). The estimated
maximum average size from this curve is very large (382 cm), which could be a result of
the scarcity of large bluefin in the data used. Recently, scientists have developed
techniques for reading ages from bluefin ear bones (otoliths); the accuracy of the age
readings has been validated with bomb radiocarbon dating. These age readings are primarily
for large bluefin (ages 5 and older), and indicate slower growth and older ages than was
previously assumed. However, an analysis of these data resulted in growth curves that
predicted very small mean sizes for the youngest age group, which could be a result of the
lack of small fish in the data used. In this study, we combine the otolith-based age
readings with the size frequency distributions of small (ages 1–3) bluefin caught by purse
seiners in the 1970s where the age groups are distinctly statistically as well as visible
to the eye. We analyzed the two datasets jointly using a maximum likelihood approach and
assumed that variability in length-at-age increases with age. The resulting growth curve
predicts sizes at young and old ages that are very consistent with observed data such as
the maximum sizes observed in the catch and the modal sizes for very young bluefin. The
resulting curve is also very similar to the curve used by ICCAT for eastern Atlantic and
Mediterranean bluefin.